In a number of today's packing and filling machines for manufacturing, for example, parallelepipedic packaging containers substantially for liquid foods, a web-shaped, flexible packaging material is progressively reformed into tube form in that both of its longitudinal edges are brought together so as to overlap and are sealed. Thereafter, the desired contents are fed to the packaging material tube and this is transversely sealed at uniform intervals in transverse sealing zones. The sealed-off sections of the tube thus filled with their contents are thereafter separated from the tube by means of incisions in the sealing zones and are formed, where applicable, by folding to the desired geometric configuration depending on how the two seals disposed transversely of the longitudinal direction of the tube have been oriented. The packaging container may, for example, be given parallelepipedic configuration.
The reforming of the originally planar packaging material into tube form takes place with the aid of a number of forming apparatuses which int.al. include forming rollers. These forming rollers are disposed annularly around a circular opening for the packaging material. The forming rollers are freely rotatable, and together force the packaging material to assume a substantially circular cross section, so that their longitudinal edges can be sealed to one another. At the last of the forming devices, the material tube has attained its final cross section and the longitudinal sealing can be carried out.
Such a forming apparatus is described, for instance in European Patent Specification EP 0 427 027.
Recently, it has become common practice to provide packaging containers with opening devices of the type comprising a pouring opening which is defined by a neck which, on its outside is provided with threading, and a cap which is disposed to be able to be threaded on and off the neck. The opening device may also include a tear-off membrane which initially covers the pouring opening and is an integral part of the neck. Many of these opening devices are applied in their entirety, by gluing or hot-melt welding, on the packaging containers when these are finally formed. However, technology is in place to injection mould the neck direct on the planar material web in holes punched specifically for this purpose. This technology is described, for instance in International Patent Publication WO 98/18609 and in U.S. Pat. No. 6,386,851. In the case involving opening devices of the type described by way of introduction, this technology is employed to injection mould the neck as well as the membrane direct on the web before the tube forming, while the cap is not applied until after the final forming of the packaging container.
On use of relatively planar opening devices, for example those which include a folding lid, and which lack the previously described neck, the above-considered technique necessitates no or extremely slight modifications to the tube forming apparatuses. Opening devices with necks and membrane, which may project roughly 10 mm out from the material web, are however not as simple to handle in the prior art forming apparatuses. As was mentioned previously, the lower, last of the forming apparatuses is dimensioned in response to the desired final diameter of the material tube and it is there that the longitudinal sealing operation takes place. When the material web with a projecting opening device is thereby to pass through said forming apparatus, the tube is forced to bulge inwards towards the centre of the tube, possibly in combination with the opening device being compressed together somewhat in order for the opening device to be able to pass. This may result in undesirable stresses on both the web and the opening device. In the upper forming apparatuses, this problem is resolved in that the roller that is placed in the path of the opening devices is permanently removed. One negative effect of this solution is that, because of the inherent rigidity of the material web, there will be a certain outward flexing of the tube in the gap. This is of no consequence in the upper early forming apparatuses. However, such an outward flexing is not desirable at the lowermost, last forming apparatus, since, with the forming of the longitudinal seal, it is important at this position to be able to maintain the cross-sectional configuration unchanged.